The present invention relates to an optical fiber array constructed by arranging and fixing an optical fiber in a V-groove and a production method thereof.
Recently, with the densification of optical fibers, movement to multifilamantary planar waveguides (PLCs) has been accelerated. Furthermore, with the movement to multifilamantary planar waveguides, development has been advanced in the direction of shortening conventional standard pitches of the waveguides so as to avoid waveguide elements from upsizing and to achieve densification. Moreover, with the densification of optical fibers and shortening of waveguide pitches, pitches between fibers of optical fiber arrays that are connected to optical fibers have been also shortened in the development of fibers.
FIG. 9 shows an example of a half-pitched fiber array whose pitches each are shortened to a half of a conventional pitch.
In FIG. 9, a lower substrate 10 having a V-groove and a coated fiber housing substrate 15 are adhesively fixed with each other from above a step portion 12 of the lower substrate 10. Coated fibers 13a and 13b are inserted with being piled in two levels from a coat housing groove 17 formed in the coated fiber housing substrate 15, and respective fibers in lower and upper levels are alternately aligned in the V-groove. Next, by attaching an upper substrate (fiber presser substrate) 11 from above the V-groove of the lower substrate 10 and fixing the upper substrate 11, an optical fiber array 22 is produced.
In the above case, after optical fibers are inserted between the upper and lower substrates, an ultraviolet hardening-type adhesive is injected into gaps of these upper and lower substrates and optical fibers. Next, ultraviolet rays are applied to harden the ultraviolet hardening-type adhesive and to fix the upper and lower substrates and optical fibers.
Although hardening of this adhesive is performed by applying ultraviolet rays to the adhesive, usually, the adhesive is hardened by applying the ultraviolet rays to the entire optical fiber array from above the optical fiber array.
Nevertheless, if the ultraviolet rays are applied to the entire optical fiber array as described above, the adhesive shrinks at the time of hardening. Therefore, since the adhesive over the entire optical fiber array is hardened at the same time, stress (distortion) corresponding to a product of the shrinkage of the adhesive used and the Young's modulus remains behind. This stress generates minute peeling within a boundary between the upper and lower substrates and adhesive, and this peeling may become a factor of degrading reliability from the long-term perspective. In addition, even if the peeling cannot be found, residual stress may exist with a high probability, and hence, such a state also has a possibility of becoming a factor raising a problem on long-term reliability.
Furthermore, in FIG. 9, a filling amount of a first adhesive between the lower substrate 10 and upper substrate 11 is largely different from that of a second adhesive injected into an upper gap (coat housing portion) of the step portion 12 that exists between the lower substrate 10 and coated fiber housing substrate 15. In consequence, there was a problem that residual stress by the shrinkage at the time of the adhesive being hardened also becomes extremely large in a second adhesive portion.